This invention claims priority of a German filed patent application DE P 198 53 092.7.
The invention relates to a receiving and supporting system for a substrate in an exposure system, which is supplied with an electro-statical chuck arrangement movable in X, Y coordinates to support the substrate on a bearing surface during exposure.
Supporting systems for the reception of substrates, especially of masks and wafers, during the time of exposure, are known in various models according to the state of art.
As a rule, those supporting systems are arranged on a table, movable in two coordinates X, Y, having a bearing area for the substrate, on which the substrate is laid prior to the exposure process and where it is held while the table step by step is moved into direction X and/or Y and where the substrate in succession is brought into the desired position of exposure.
In most cases, the bearing levels are formed with high-plane bearing surfaces, possibly also with several punctiform bearing elements.
The basic bodies, mounting plate, etc., on which the bearing elements are positioned or bearing surfaces are formed, are in most cases mechanically affixed to the table via metering means for the positioning of the substrate in Z coordinate. The Z coordinate thereby corresponds to the exposure direction of the exposure beam-path, directed right-angled onto the substrate""s surface.
The sensitive handling of the substrate during the receiving phase into the exposure system, and the precision during the positioning of the substrate surface relative to the exposure system are substantial criterion in regard to the quality and sensitivity of structure during exposure and increasing importance, as far as future attempts of the micro-electronic industry for the reduction of structure dimensions are concerned.
Since the substrate itself is not stable against deformations, the main problems with these versions of supporting systems appear in the precision of the positioning for the substrate, even in case of temperature-or pressure variations, as well as in the dimensional shape of the substrate support.
Therefore it has to be taken into account, that no mechanical force, regardless what origin, is influencing the substrate, which would lead to deformations and therefore unacceptable deviations in structure.
Furthermore, for the construction of supporting systems it has to be considered, that the direction of the exposure beam is not unintentionally influenced by magnetic fields and/or electric power charges. Above all, the manufacturing of supporting systems must be kept within economically reasonable limits.
In consideration of these high requirements, the supporting systems according to the state of art need to be evaluated.
The U.S. Pat. No. 5,535,090 and the publication xe2x80x9cSemiconductor Internationalxe2x80x9d, Sherman, Vol. 20, No. 8, p. 319-322 for example announce a decive, with electro-static chuck arrangement for the support of substrates during exposure. The chuck arrangement shows a conductive layer, which can be applied to the substrate via electrical supply contacts with electrical switch-off potentials. In case of potential application, an electro-static field develops, by means of which the substrate is held on a plane insulation layer, positioned above the conductive layer. In this case, the extent of the force of attraction between the chuck arrangement and the substrate is dependant upon the electrical voltage applied, the size of the conductive layer, (the so called chuck electrode), and the thickness of the insulation layer, located between the conductive layer and the substrate.
To avoid unintentional influence of the exposure beam path, appropriate measures have to be taken to prevent electro-static charging at unwanted locations of the supporting system or the exposure system, when applying electro-static chuck arrangements in exposure systems.
An appropriate measure is for example the use of non-magnetic materials. This is achieved in the described arrangement of the mentioned publication by using sapphire material.
Sapphire admittedly is non-magnetic, however the costs for purchase are extremely high and consequently the technological costs for the production of the plane bearing surface for the substrate are immense. Therefore, in the arrangement mentioned above, the 8xe2x80x3 sized bearing surface has not completely been covered with sapphire material, but several 2xe2x80x3 sized sapphire plates have been arranged via an intermediate layer of Niob. Disadvantageous in this case is the technologically elaborate manufacturing procedure for a multi-layer bearing surface.
In addition to this, the uniformity of the material, carrying the substrate, is not guaranteed, resulting in a non-uniformity of the supporting power as far as the entire bearing surface is concerned.
The U.S. Pat. No. 5,600,530 also describes a supporting device for substrates, where once again an electro-static chuck arrangement is provided. In this case, however, the material used for the insulation layer of the chuck arrangement is aluminium oxide, and the invention furthermore describes a procedure, in which the thick aluminium oxide layer is thinned down to the appropriate thickness. Due to its unfavourable properties in temperature-fluctuations, the use of aluminium oxide leads to detrimental problems. For the compensation of this disadvantage, the use of aluminium oxide to manage a high exposure accuracy leads to extensive measures in order to avoid positioning errors and/or deformations of the substrate on the aluminium oxide layer. A solution for this problem, resulting from the use of aluminium oxide, however, is no described in the mentioned patent.
Another substrate receiving device for treatment in an electron-beam-system is disclosed in U.S. Pat. No. 5,644,137. The arrangement described here, is equipped with interferometers for the positioning and observation of the table and so of the substrate during the movement in X, Y coordinates. A stabilisation of the substrate""s position relative to the exposure system is reached, as some parts of the supporting system and the interferometer mirrors are manufactured from material of equal expansion-behaviour, resulting in a higher positioning precision in the directions X and Y.
Unfortunately, this patent does not mention any means and measures to solve the problem of material expansion in direction to coordinate Z, or the imprecision resulting from this.
Another disadvantage in the publications mentioned above, is the fact that the supporting systems do not provide technical feeding devices that enable the receiving of the substrate via e.g. a robot arm and its sensitive and exact positioning on the deposit area.
It is therefore the object of the invention to develop supporting systems in the abovementioned style with further improvements to facilitate a precise receiving from a handling system and a better positioning and shape stability during the exposure.
For a receiving and supporting unit of the abovementioned style, this task is solved through the characterizing features of claim 1. Further advantageous improvements are indicated in features of the sub-claims.
The receiving and supporting unit of the abovementioned style provides at least a second electrostatic chuck arrangement, whichxe2x80x94similar to the first electro static chuck arrangement, that supports the substrate during exposure,xe2x80x94provides a bearing surface for the substrate, whereby the bearing surface of the first chuck arrangement und the bearing surface of the second chuck arrangement mutually form a bearing surface for the substrate, and whereby the bearing surface of the second chuck arrangement is positioned in Z direction, that is to say in the direction of the exposure light beam-path , relatively moveable to the bearing surface of the first chuck arrangement.
In regard to their holding force, both chuck arrangements are designed to support the substrate in a save position while placing it either on the first chuck arrangement or exclusively on the second chuck arrangement.
The arrangement in this invention offers the advantage, that both chuck arrangements can be counter-shift along the Z-direction, which renders possible to move the bearing surface of the second chuck arrangement up to receiving position Z2, in which a robot arm keeps ready for take over into the exposure system. The receiving position Z2 for instance is located in a distance xcex94z from the bearing surface of the first chuck arrangement, which constantly remains in position Z1.
For a precise verbal distinction between the first and the second chuck arrangement, the term xe2x80x9csupporting chuckxe2x80x9d will subsequently be used for the first chuck arrangement, the term xe2x80x9chandling chuckxe2x80x9d for the second chuck arrangement, in accordance with their respective functions.
During operation of the receiving-and supporting system acc. to the invention, the handling chuck in position Z2, moved out of the supporting chuck, takes over the substrate for instance from a robot arm and after the electro-static holding force between the handling chuck and the substrate has become effective, the handling chuck then is being moved back at least in a position, in which the bearing surface of both chucks forms a mutual plane in position Z1.
Since the bearing surface of the handling chuck is smaller than the substrate""s surface to be supported, free sections of the substrate superimpose the bearing surface of the handling chuck. Not until the handling chuck has moved its bearing surface back toward position Z1, the substrate with its free surface sections comes into contact with the bearing surface of the supporting chuck and is positioned on both,xe2x80x94the bearing surface of the supporting chuck as well as the handling chuck, provided that the handling chuck remains in position Z1. The invention provides another method of implementation, in which the handling chuckxe2x80x94after moving backxe2x80x94remains in position Z1, in which the substrate is placed in exposure position and lies partly on the bearing surface of the supporting chuck and partly on the bearing surface of the handling chuck. In this position Z1, the handling chuck can alternatively be fixated through a clamp device or remains non-fixated in position Z1.
In the latter case, the bearing surface of the handling chuck is freely moveable into Z direction andxe2x80x94as soon as the electro static holding force between the supporting chuck and the substrate is effective, due to the strainxe2x80x94equalizing forces, performed by the substrate and provided that the two bearing surfaces are not in a mutual plane,xe2x80x94it can be pulled back into position Z1, in which the bearing surface of the supporting chuck is positioned.
In regard to an exact positioning of the handling chuck in position Z1, this method advantageously and without intensive technical requirements provides the strain-free support of the substrate without any risk of deformation.
However, another variant of the invented receiving and supporting system contains the possibility to disconnect the handling chuck from the substrate after locating the substrate on the bearing surface of the supporting chuck, and retract the handling chuck into position Z2xe2x80x2, which applies to Z2xe2x80x2 less than Z1 less than Z2. In this case, the substrate merely lies on the bearing surface of the supporting chuck during exposure, while a free space remains between the bearing surface of the handling chuck and the substrate.
Another especially preferable variant of the invention may provide, that the bearing surfaces of both chuck arrangements are aligned parallel to the direction of earth""s gravity influence, namely that for example the Y coordinate is positioned in the direction of the gravity influence while coordinate X, Z proceed right-angled to the gravity direction. In regard to the handling and positioning of the substrate, various advantages result from this method, which will be described in the following.
In connection with the vertical alignment of the bearing surfaces, in accordance with the invention, it is furthermore intended, that the two chuck arrangements are connected to a lifting device, which is moveable into direction of the Y coordinate, whereby the supporting chuck is fixated through a mounting plate, while the handling chuck is coupled with the lifting device through a linear adjusting drive, (moveable in direction Z).
In this way it is accomplished, that the two chuck arrangements with their vertically aligned bearing surfaces as well as the supported substrate can be adjusted by means of raising and lowering the lifting device into Y direction, keeping the distance to the exposure optic constant. Therefore it is intended to arrange the lifting device on a column, which is positioned parallel to coordinate Y, and to adjust the lifting device along this column linearly guided through skids and/or rollers, whereby in addition to the skids and/or rollers, piezo-electrically driven clamp devices for occasional click-stop detents of the lifting device at the column are provided.
During the exposure cycle for example, the lifting device then may be locked in its position directed to Y coordinate.
The column is connected to at least one X-carriage, by means of which the supported substrate can be moved in X-direction, constantly spaced to the exposure optic. It is therefore ensured, that each area fraction of the substrate can be brought into exposure position, on the one hand via movements of the lifting device in Y-direction and/or on the other hand via movement of the carriage in X-direction.
In another variant of the invention it can be provided, that the linear drive for the handling chuck is equipped with a pneumatic drive, such as a bellow or a membrane. These versions of pneumatic drives are well known in technique nowadays and therefore needn""t be described precisely.
Another advantageous version of the invented arrangement renders possible to arrange the two chuck arrangements in a circular and concentric manner to each other, whereby the bearing surface of the handling chuck is encircled by the bearing surface of the supporting chuck, having an expansion of less ⅓, preferably less xc2xc of the bearing surface of the supporting chuck
Thus guarantees, that the substrate, when supported on the handling chuck, exceeds the bearing surface laterally in a sufficient degree, and an adequate amount of projecting fractions of the substrate can be positioned on the bearing surface of the supporting chuck during the return phase.
According to the invention, it is furthermore provided, that each chuck arrangement consists of a basic body on which,xe2x80x94at least partlyxe2x80x94an electrically conductive layer is deposited having an insulation layer above it, whereby the insulation layer is positioned towards the exposure optic, forming the bearing surface for the substrate.
Channels for a cooling medium may be built into the insulation layers, leading to inlets/outlets of the cooling medium, using helium as a preferable coolant.
In a very advantageous version, the mounting plates and the basic bodies of the chuck arrangements are made of glass-ceramic with the same material properties, for example with equal thermal expansion coefficient xcex1T=0xc2x10.05*10xe2x88x926Kxe2x88x921, equal modulus of elasticity of E≈90.6 GPa and equal tensile strength of B about 130 MPa.
The utilisation of such glass ceramic for the parts in question allows a supporting system design, which is exceptionally insensitive to temperature-fluctuations. Since temperature- influences within the arrangement during the exposure cycle is technically inevitable, using those glass ceramics reduce the negative effects to an extent, that additional temperature-stabilizing measures within the exposure arrangement or temperature-stabilizing measures in the vicinity of the substrate to be exposed, can be reduced to a minimum.
A further essential advantage of glass ceramic is that conventional optic processing technologies during the production of the parts in question can be applied, through which effectively a maximum degree of accuracy can be obtained during processing. This refers especially to the fabrication of plane surfaces with maximum planeness requirements, but also in respect of keeping parallelisms and angles of the respective parts. This renders possible to meet manufacturing tolerances within the range of micrometer of arc seconds. Due to the brittle hardness of the implemented glass ceramics, plastic deformations of the plane surfaces, especially of the bearing surfaces of the substrate are excluded, whereby permanent deformations, caused by mechanical forces, cannot influence the substrate.
The skids and/or rollers for guidance of the lifting device and also the column are of a highly strong ceramic with a modulus of elasticity in the range of 300 to 400 GPa. Therefore, an accurate guidance of the lifting device along the column can be obtained. In addition to the skids and/or rollers, electrically driven clamp devices for at-times click-stop detents of the lifting device are provided, respectively in those positions, where the exposure of the substrate surface will be carried out.
With the utilization of glass ceramic respectively ceramic materials for the named parts, it is obtained, that the exposure beam path is not accidentally influenced by magnetic fields, since these materials are non-magnetic.
Besides, it is another advantage that these materials can be provided in a technologically simple manner with an electrically conductive layer, for example chrome or nickel, which can be supplied with an electric voltage potential. For a save support of the substrate on the bearing surfaces of the two chuck arrangements it is intended to attach an electric potential with up to 5000 Volts to the conductive layers on the one hand and at the substrate on the other hand.
In another very beneficial version of the invention it is provided, that two mirrored surfaces are attached to the mounting plate, one of which is directed to X-coordinate and the other is directed Y-coordinate, both serving as reference mirror of a meteorology system, in which the determination of the position of the mounting plate respectively to the substrate is carried out by interferometric measurings.
The mirrored surfaces can be an aluminium layer, supplied with an oxide protective layer, preferably SiO2.
Furthermore, the mounting plate may show material recesses, which lead to a reduction in weight, advantageously resulting in lower driving forces as well as favourable acceleration behaviour during movement of the lifting device. Another variant is to attach the basic body of the first chuck arrangement either directly to the lifting device, or, alternatively connect it to the lifting device via a mounting plate.